The present invention relates to a process for the preparation of terpenic ketones. More particularly, it relates to the preparation of terpenic ketones from 1,3-butadiene which may be substituted on the carbon atom 2 by a hydrocarbon chain, preferrably a polyene chain and more preferably an isoprene chain. The terpenic polyene ketones are of the following general formula: ##STR1## in which n is an integer from 1 to 4.
European Patent 33,771 describes the condensation reaction of a compound having an activated carbon atom with a conjugated substituted diene. The conjugated substituted diene may be a 1,3-butadiene substituted on the carbon atom 2 by a hydrocarbon chain. The compounds having an activated carbon atom may be selected, for example, from aldehydes, ketones, esters, sulphonic esters, nitrate derivatives, cyano derivatives and amides. The products of the condensation reaction are compounds in which the activated carbon atom is substituted with the conjugated substituted diene. These products serve as precursors for vitamins A and E or can be used in perfumes.
The decarboxylation of .beta.-keto esters by means of a medium composed of water and dimethyl sulphoxide is described by Krapcho et al., J. Org. Chem., 43, pages 143, (1978). However, this paper does not describe the decarboxylation of .beta.-keto esters substituted by a terpene group such as isoprene. The decarboxylation reaction described in this paper suffers from the use of a solvent such as dimethyl sulphoxide which the industry tries to avoid because it is expensive and hazardous.
J. M. Derfer et al. (Kirk Othmer, 22, page 731) describe the preparation of geranylacetone, which is a terpenic ketone, by transesterification of linalool with ethyl acetoacetate according to the Carroll reaction by the elimination of carbon dioxide. This reaction, however, is specific for linalool. Because linalool is an expensive raw material, there has been long-felt need for a means of access to vitamins which avoid the use of linalool as a starting material.